I am using the .NET Developer Bundle which contains VS 2010/2012 integration.

I recently (today) installed the latest ReSharper, version 8. After installation and launching either VS2010 or VS2012, the .NET Reflector menu is present however the ANTS menu is gone...

My question is how can I quickly restore the ANTS menu without reinstalling the bundle? If reinstall is required, do I have to 'Deactivate the Serial Numbers' beforehand or is the installer smart enough to retain my license?

You may be able to avoid a reinstall if you open VS, go to Tools->options->add-in security, and (if it's missing) re-add a path to the "ANTS Profiler Visual Studio Add-in 1" there (the path should be c:\\program files\\red gate\\ants profiler visual studio add-in 1\\), and make sure that that folder has the RedGate.ANTSVsAddin.addin file and the RedGate.ANTSVsAddin.dll.

Should that not help though, please do try a reinstall of just the add-in-- your license should be retained

Deleting the registry key worked. The menu was restored after the deleting the key and restarting VS2010/2012.

Suggestion:
Your add-in should be more reactive when integrating with the menu. If its static location (which you store in the registry) is not found due to other 3rd party tools being installed/uninstalled, don't give up. Determine a new menu location and update the registry instead of giving up and not displaying a menu.